This invention relates generally to blowers of the Roots type having multiple-lobe rotors and more particularly to a Roots type blower in which, by reducing the variation of the clearance gap between the rotors to a minute value, the volumetric efficiency of the blower is improved.
As is known, Roots type blowers are often used as air or gas blowers for industrial equipment, for example, because of their advantageous features such as simple construction and low frequency of mechanical failure.
A typical conventional blower of this Roots type comprises essentially a housing having a rotor chamber and intake and delivery ports on opposite sides of the rotor chamber, at least one pair of first and second rotors of substantially the same shape and the same radius, and rotatable rotor shafts on which respective rotors are fixedly supported, and which are parallelly disposed at a specific center-to-center spacing distance. Each rotor has at least two blade-like projections each comprising a lobe of convex arcuate profile as viewed in plan view forming the outer projecting part and halves of hollow recess of concave arcuate profile on opposite flank sides of the lobe, the lobes and the recesses being of the same number and being formed alternately and contiguously around the rotor. The radius of the convex arc of the lobes is substantially equal to the radius of the concave arc of the recesses. As described more fully hereinafter, the configuration of the two rotors are so designed that, as the rotors in assembled state rotate, the lobes of each rotor mesh closely but freely with respective recesses of the other in the manner of the teeth or cogs of a pair of enmeshed gears.
In the operation of this blower, the rotors are rotated in mutually opposite direction such as to cause air to be transported mechanically from the intake port, around the outer unmeshed parts of the rotors within the rotating spaces formed between the above described recesses and the semicylindrical inner wall surface of the rotor chamber of the blower housing, and into the delivery port. The parts of the rotors which have thus transported the air then mesh with one another and rotate from the delivery side to the intake side to cyclically repeat the air transporting operation.
For reasons which will be described more fully hereinafter, a certain clearance gap is provided between the confronting surfaces of the enmeshing parts of the rotors so as to prevent binding and ensure smooth action. This clearance gap, which varies with various factors, principally the configuration of the rotor profile, unavoidably permits air to leak therethrough from the delivery side to the intake side. Therefore, in order to obtain a high volumetric efficiency of the blower, this air leakage must be reduced to a minimum. The Roots type blowers in the prior art have not been fully satisfactory in this respect, being accompanied by a number of problems